Making Discrete Solid Particles of Polymeric Material

ABSTRACT

A process is provided for producing discrete solid beads of polymeric material e.g. phenolic resin having a mesoporous structure, which process may produce resin beads on an industrial scale without aggregates of resin building up speedily and interrupting production. The process comprises the steps of: (a) combining a stream of a polymerizable liquid precursor e.g. a novolac and hexamine as cross-linking agent dissolved in a first polar organic liquid e.g. ethylene glycol with a stream of a liquid suspension medium which is a second non-polar organic liquid with which the liquid precursor is substantially or completely immiscible e.g. transformer oil containing a drying oil; (b) mixing the combined stream to disperse the polymerizable liquid precursor as droplets in the suspension medium e.g. using an in-line static mixer; (c) allowing the droplets to polymerise in a laminar flow of the suspension medium so as to form discrete solid beads that cannot agglomerate; and (d) recovering the beads from the suspension medium. Also provided is an apparatus for forming discrete solid beads of polymeric material. In other embodiments, a method is provided for carbonizing and activating carbonaceous material, and an externally fired rotary kiln for carbonizing and activating carbonaceous material.

FIELD OF THE INVENTION

This invention relates to a process which can be operated on anindustrial scale for the manufacture of organic resins in bead form fromliquid precursors that undergo rapid polymerization under intendedconditions. It is particularly, but not exclusively concerned with theproduction of beads of resin that may be carbonized to form beads ofcarbon, although the resin beads formed may have other utilities e.g. asion exchange resins. The invention also provides apparatus for formingdiscrete solid beads of polymeric material in which in some embodimentsthe above mentioned process can be implemented. The invention provides amethod and apparatus for carbonizing and activating carbonaceousmaterial which is particularly, but not exclusively suitable forcarbonization and activation of the above mentioned resin beads. Theinvention also provides a method and apparatus for making activatedcarbon.

BACKGROUND TO THE INVENTION Production of Polymer Beads

The production of polymer beads by controlled droplet coalescence in alaminar liquid stream followed by dispersion polymerization in adescending column of liquid to produce hardened beads which aresubsequently further heated for 6-8 hours to complete polymerization isdisclosed in U.S. Pat. No. 4,424,318 (Vairetti et al.). The beads are acopolymer of styrene and divinylbenzene, and the dispersion medium isaqueous calcium chloride containing bentonite and sodiumlignosulphonate. The process is inapplicable to rapidly polymerizingmixtures owing to the prolonged coalescence stage, there is nodisclosure or suggestion that polymerization can be completed in alaminar flow column, nor is there any suggestion that the dispersionmedium can be other than aqueous. The knowledge and belief of theinventors is that the Vairetti process has not been commercialized andthat production of styrene/divinylbenzene beads remains a stirred batchprocess.

Preparation of Beads of Inter Alia Styrene/Divinylbenzene Copolymer isAlso disclosed in U.S. Pat. No. 6,492,471 (Eisenbeiss et al. Merck)where it is explained that the problem of producing bead polymers on alarge industrial scale remains unsolved. The reasons include mixingproblems, problems in obtaining a desired bead size distribution and theformulation of caked aggregates in dead spaces. The disclosed solutionis to use high performance micromixers. The continuous phase is water,water/alcohol or water/organic solvent and the dispersed phase is ahydrocarbon or sparingly water-miscible hydrocarbon which contains themonomer or monomers to be polymerized. Particular preference is given tothe so-called LIGA micromixing system (micromixer) from IMM (Institutfur Mikrotechnik Mainz GmbH) in which two liquid streams are transportedin opposite directions to one another in specially shaped microchannelsin a mixing unit and subsequently discharged through a slotperpendicular to the flow direction. Production of particles of size0.1-300 μm is envisaged, more typically 1-20 μm or 10-50 μm, and theformation of larger droplets is not disclosed. The use of micromixers isinappropriate for polymerizable liquid precursors whose rate ofpolymerization is relatively rapid at the intended mixing temperaturebecause in such mixers the size of the channels is the same as that ofthe beads produced and there is a high probability of the mixer beingblocked by accumulating deposits of polymer. Furthermore, the use oflaminar flow conditions for polymerization of the dispersed droplets isneither disclosed nor suggested.

A problem with which this invention is concerned is to provide a processwhich can produce resin beads on an industrial scale without aggregatesof resin building up speedily and interrupting production.

Production of Mesoporous Beads

That problem has become relevant to the present applicants who areseeking to produce on an industrial scale mesoporous beads of phenolicresin as intermediates in the production of beads of carbon having amesoporous/microporous pore structure.

WO 02/12380 (Tennison et al., the disclosure of which is incorporatedherein by reference) discloses making a mesoporous resin by condensing anucleophilic component which comprises a phenolic compound or a phenolcondensation prepolymer with at least one electrophilic cross-linkingagent selected from formaldehyde, paraformaldehyde, furfural andhexamethylene tetramine in the presence of a pore-former selected fromthe group consisting of a diol (e.g. ethylene glycol), a diol ether, acyclic ester, a substituted cyclic ester, a substituted linear amide, asubstituted cyclic amide, an amino alcohol and a mixture of any of theabove with water to form a resin. The pore-former is present in anamount effective to impart mesoporosity to the resin (e.g. at least 120parts by weight of the pore former being used to dissolve 100 parts byweight of the nucleophilic component, which corresponds to 100 parts byweight of the total resin forming components, i.e. nucleophilcicomponent plus electrophilic component), and it is removed from theporous resin after condensation by washing or by vacuum drying. Theresulting resin may be carbonised by heating in an inert atmosphere to atemperature of at least 600° C. to give a material having a bimodaldistribution of pores, the pore structure as estimated by nitrogenadsorption porosimetry comprising micropores of diameter up to 20 Å andmesopores of diameter 20-500 Å, and the material also containingmacropores. The value for the differential of pore volume with respectto the logarithm of pore radius (dV/d log R) for the mesopores isgreater than 0.2 for at least some values of pore size in the range20-500 Å The mesoporous carbon may have a BET surface area of 250-800m²/g without activation. It may be activated by heating it at hightemperature in the presence of carbon dioxide, steam or a mixturethereof, e.g. by heating it in carbon dioxide at above 800° C., or itmay be activated by heating it in air at above 400° C. It may then havesurface areas of up to 2000 m²/g. As used herein the term “BET surfacearea” is determined by the Brunauer, Emmett, and Teller (BET) methodaccording to ASTM D1993-91, see also ASTM D6556-04.

In WO 02/12380, production of the resin in both powder and bead form isdisclosed. Production of the bead form may be by pouring partiallycross-linked pre-polymer into a hot liquid such as mineral oilcontaining a dispersing agent and stirring the mixture. The pre-polymersolution forms into beads which are initially liquid and then, as curingproceeds, become solid. The average bead particle size is controlled byseveral process parameters including the stirrer type and speed, the oiltemperature and viscosity, the pre-polymer solution viscosity and volumeratio of the solution to the oil and the mean size can be adjustedbetween 5 and 2000 μm, although in practice the larger bead sizes aredifficult to achieve owing to problems with the beads in the stirreddispersion vessel. The beads can then be filtered off from the oil. In apreparative example, industrial novolac resin is mixed with ethyleneglycol at an elevated temperature, mixed with hexamine and heated togive a viscous solution which is poured into mineral oil containing adrying oil, after which the mixture is further heated to effect curing.On completion of curing, the reaction mixture is cooled, after which theresulting mesoporous resin is filtered off, and washed with water toremove pore former and a small amount of low molecular weight polymer.The cured beads are carbonized to mesoporous carbon beads which have apore structure as indicated above, and may be activated as indicatedabove. It is stated that the beads can be produced with a narrowparticle size distribution e.g. with a D90.D10 of better than 10 andpreferably better than 5. However, the bead size distribution that canbe achieved in practice in stirred tank reactors is relatively poor, andthe more the process is scaled up the worse the homogeneity of themixing regime and hence the particle size distribution becomes.

Patent Application WO 2006/103404 (Cashmore et al., British AmericanTobacco Co, the disclosure of which is incorporated herein by reference)discloses that the above mesoporous carbon beads are suitable forincorporation into smoke filters of cigarettes, and that carbonizedresins obtained from phenoloc resins cross-linked by nitrogen-containingcross-linking agents e.g. hexamethylenetetramine or melamine or producedfrom nucleophilic precursors such as amno phenols are particularlyeffective for removing hydrogen cyanide from the vapour phase of tobaccosmoke, and also perform well in the removal of formaldehyde,acetaldehyde and 1,3-butadiene. Porous carbon in the form of microbeadse.g. of size 50-1000 μm is said to be particularly suitable for handlingin the manufacture of smoking articles because the microbeads have areduced risk of sticking together and giving rise to uneven loading ofabsorbent material tow for forming into cigarette filters, and becausethey have a low attrition rate and therefore generate less dust ascompared to known forms of carbon e.g. coconut charcoal.

A more specific problem with which the invention is concerned istherefore the production of mesoporous beads of phenolic resin on anindustrial scale without rapid formation of aggregates of polymerizedmaterial that would interfere with production.

Bead Carbonization and Activation

Both carbonization and activation of carbonaceous materials in rotarykilns is known, but the processes involved in practical production areslow and the materials produced vary in their properties.

U.S. Pat. No. 1,505,517 (Woodruff et al.) discloses the activation ofcarbon in a rotary kiln rotating at about 1 revolution every 2 minutes,inclined at a small angle to the horizontal and provided with flightswhich serve both to agitate the material within the kiln and to elevatethat material and drop it through the kiln atmosphere, the preferredactivating material being steam, although the use of carbon dioxide isalso mentioned. Treatment of highly flowable materials in bead form isnot disclosed and no means is provided for retarding the flow ofmaterial through the furnace and hence of controlling residence time.

U.S. Pat. No. 4,344,821 (Angelo) discloses a process for simultaneousdrying, carbonization and activation of carbonaceous material of animalor vegetable origin in a rotary kiln. It is explained that once thecarbonization reaction is initiated, it is self-sustaining, but thatthat the heat generated is insufficient to dry the incoming material.Air is introduced into the kiln to partially combust the gases given offduring carbonization and hence provide the heat needed for the dryingstage. The present inventors are of the view that any introduction ofair into the kiln is to be avoided, especially in the case of mesoporousmaterials. For activation, superheated steam is injected at the lowerend region of the kiln directly into the bed of char for the purpose ofactivating the char without steem circulating into the region above thebed. Again, treatment of highly flowable materials in bead form is notdisclosed and no means is provided for retarding the flow of materialthrough the furnace and hence of controlling residence time.

U.S. Pat. No. 6,316,378 (Gibelhausen et al., CarboTex GmbH) is concernedwith the production of carbon beads from resinous raw materials e.g. ionexchange beads using a rotary tunnel dryer. In an example, resin wassupplied to a rotary drying kiln having a length to diameter ratio of5.5 to achieve a filling level of 20%, the kiln having lift scoops forturning over the product and the product having a transport speed of11.1 cm/minute, drying being in a countercurrent of hot gas.Carbonization and activation were then carried out in a rotary tunnelkiln filled to a filling ratio of 11%, having a co-current flow of steamand employing temperatures of 850-900° C. The kiln had a length todiameter ratio of 12, the transport speed of the product was 28cm/minute, the residence time was 514 minutes, and the steam wasintroduced about 20% of the distance along the kiln. The discloseddrying conditions would destroy mesoporosity in the resin beads.According to the calculations of the present inventors, the dryer lengthwas 5 meters, the pyrolysis region was 36 meters long and the activationregion was about 144 meters long. Although the kiln sloped downwardly,it must have been at a very shallow angle owing to its length, and thereis no disclosure or suggestion of annular weirs to control the flow ofbeads along the furnace and hence the residence time.

SUMMARY OF THE INVENTION

That problem may be solved, according to the invention, by a process forproducing discrete solid beads of polymeric material, said processcomprising the steps of: (a) forming a combined stream from a stream ofa polymerizable liquid precursor and a stream of a liquid dispersionmedium with which the liquid precursor is substantially or completelyimmiscible; (b) treating the combined stream so as to disperse thepolymerizable liquid precursor as droplets in the dispersion medium; (c)allowing the droplets to polymerise in a laminar flow of the dispersionmedium so as to form discrete solid beads that cannot agglomerate; and(d) recovering the beads from the dispersion medium, the dispersivetreatment time being short compared to the laminar flow polymerizationtime so that agglomeration of the liquid precursor during dispersivetreatment is substantially avoided.

There is no simple numerical definition of the relationship betweendispersive treatment time and laminar flow polymerization time, becausethis will vary between one reactive component system and another andwill depend on the nature and amount of solvent in the polymerizableliquid precursor and on the temperatures used. However, in someembodiments the dispersive treatment time is <5% of the laminar flowpolymerization time, more preferably in some embodiments <2% and stillmore preferably in some embodiments <1%. In a laminar descending flowpolymerization column which is employed in embodiments of the invention,the laminar flow polymerization time can be considered to be the averagetime for dispersed droplets to pass down the column.

There is also provided apparatus for forming discrete solid beads ofpolymeric material, said apparatus comprising: a first line forconveying a stream of a polymerizable liquid precursor; a second linefor conveying a stream of a dispersion medium with which thepolymerizable liquid precursor is substantially or completelyimmiscible; an in-line mixer configured to receive a combined flow fromthe first and second lines and to disperse the polymerizable liquidprecursor as droplets in the dispersion medium; a verticalpolymerization column configured to receive the dispersion medium withthe droplets dispersed therein and to permit the polymerizable liquidprecursor polymerize while descending the column in a descending flow ofpolymerization medium; and a vessel at the base of the column forreceiving the descending flow of dispersion medium and collectingpolymerized solid beads.

Embodiments of the apparatus further comprise: first and second vesselsfor storage of first and second liquid components of the polymerizableliquid precursor; first and second component lines for conveying theliquid components; first and second non-pulsating pumps in said linesfor conveying component streams through the lines; and a second in-linemixer configured to receive and mix the streams of the first and secondcomponents and to form a polymerizable liquid precursor stream.

A heater may be provided in one or both of the first and secondcomponent lines for heating one or both of the streams flowing to thesecond in-line mixer. The apparatus may further comprise a storagevessel for dispersion medium, a line leading from the storage vessel tothe in-line mixer, and a third non-pulsating pump in said line forconveying a stream of dispersion medium. The dispersion medium line maycomprise a heat exchanger for heating the stream of dispersion mediumfrom the storage vessel, the apparatus may further comprise a thirdin-line mixer configured to receive heated dispersion medium from theheat exchanger and to supply dispersion medium that has passed throughit to the first in-line mixer, and the vessel at the base of the columnmay be a stirred tank or it may be a settling tank having an outlet forbeads forming a sediment in said tank.

The invention further provides a method for carbonizing and activatingcarbonaceous material, which comprises supplying the material to anexternally fired rotary kiln maintained at carbonizing and activatingtemperatures, the kiln having a downward slope to progress the materialas it rotates, the kiln having an atmosphere substantially free ofoxygen provided by a counter-current of steam or carbon dioxide, andannular weirs being provided at intervals along the kiln to controlprogress of the material.

In a further aspect the invention provides an externally fired rotarykiln for carbonizing and activating carbonaceous material having ahollow rotary body that has a downward slope towards a discharge endthereof, and which is provided at intervals along its length withannular weirs for controlling progress of the carbonaceous material.

In another aspect, the invention provides a method of preparingactivated carbon by subjecting char in a rotary furnace at an elevatedtemperature to an atmosphere of activating gas, wherein annular baffleswithin the furnace define treatment zones in sequence along the furnace,and wherein fresh char entering the furnace causes material beingactivated to overflow the baffles from one treatment zone to the next.

In yet another aspect, the invention provides a method of preparingactivated carbon by subjecting char in a rotary furnace at an elevatedtemperature to an atmosphere of activating gas, wherein annular baffleswithin the furnace define treatment zones in sequence along the furnace,and wherein fresh char entering the furnace causes material beingactivated to overflow the baffles from one treatment zone to the next,and wherein lift bars located in the treatment zones lift portions ofbeds of the char as the furnace rotates and then permit char to cascadethrough the activating gas atmosphere and to return to the bed.

BRIEF DESCRIPTION OF THE DRAWINGS

How the invention may be put into effect will now be described, by wayof example only, with reference to the accompanying drawings, in which:

FIG. 1 is a simplified flow sheet for a first embodiment of apparatussuitable for production of polymer beads;

FIG. 2 is a schematic diagram of a polymerization column assemblyforming part of the apparatus of FIG. 1;

FIG. 3 shows the pore size distribution data of four samples of resinprepared by the method of the invention (DV/D Log R versus mean poresize (A));

FIG. 4 is a perspective view of the mixing elements of an in-line mixerforming part of the apparatus of FIGS. 1 and 2 additionally showing ashort length of the mixer casing;

FIG. 5 is a simplified flow sheet for a second embodiment of apparatussuitable for production of polymer beads and FIG. 5 a is a detail of anoverflow tank forming part of the apparatus of FIG. 5. (Parts in FIG. 5and having the same function as those in FIG. 1 are labelled so far aspossible with reference numerals which are the same as in FIG. 1 butincremented by 100, so that the tank 10 in FIG. 1 is labelled as tank110 in FIG. 5);

FIG. 6 is a diagrammatic view of a treatment kiln for solvent removal,carbonization and activation according to an embodiment of theinvention; and

FIG. 7 is a view of the kiln of FIG. 6 looking into the kiln body.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

As used herein, the term “microporous” refers to a carbon or othermaterial possessing pores with diameter <2 nm, as measured by nitrogenadsorption and mercury porosimetry methods and as defined by IUPAC.

As used herein, the term “mesoporous” refers to a carbon or othermaterial possessing alongside micropores, pores with diameter from ca. 2nm to ca. 50 nm, as measured by nitrogen adsorption and mercuryporosimetry methods and as defined by IUPAC.

As used herein, the term “macroporous” refers to a carbon or othermaterial possessing alongside micropores pores with diameters largerthan 50 nm, as measured by nitrogen adsorption and mercury porosimetrymethods and as defined by IUPAC.

Embodiments of the invention relate to the formation of cured resinbeads from liquid precursors that become polymerizable by combinationand mixing of first and second component streams to give a combinedstream that after dispersion in liquid suspension medium at or close tothe intended polymerization temperature undergoes substantially completepolymerization within a short time period e.g. 0.2-5 minutes e.g. 0.5-4minutes. Problems in the handling of such reaction systems include:

-   -   effective mixing of the first and second component streams;    -   effective dispersion of the liquid precursor in the dispersion        medium to give droplets of desired size with a desired range of        droplet sizes and to complete the dispersion step within a time        that is short compared to the polymerization time so that        unintended increases in viscosity and/or deposition of        agglomerated materials are substantially avoided; and    -   conducting polymerization under conditions such that the beads        formed neither break up nor aggregate during polymerization and        when collected have hardened sufficiently that they will not        aggregate even when in mutual contact.

The present process, when used to make mesoporous activated carbon, maycomprise the following successive steps:

1. Combine and mix components to form polymerizable liquid precursor.

2. Disperse polymerizable liquid precursor as droplets in a dispersionmedium.

3. Polymerize liquid precursor droplets in laminar flow of dispersionmedium.

4. Recover resulting beads from dispersion medium

5. Wash beads

6. Vacuum dry beads

7. Heat treat beads to remove residual solvent

8. Carbonise beads

9. Activate carbonised beads.

For the production of material other than mesoporous activated carbon,e.g. ion exchange material, the above sequence of steps may beterminated after washing the beads. For the treatment of materials otherthan resin beads e.g. coconut-derived or other vegetable materials, theheat treatment, carbonization and activation steps are performed.

Mixing and Dispersion

It will be appreciated that the polymerizable liquid precursor sees twomixing operations, firstly mixing of its component streams 114, 122(FIG. 5) in a first mixer and secondly dispersion of the resulting mixedstream 126 into the dispersion medium in a second mixer 418. Similarlythe dispersion medium also sees two mixing operations, firstly mixing ofa third dispersing agent stream 134 with a fourth dispersant stream 140in a third mixer 146 and secondly dispersion within it of thepolymerizable liquid precursor stream in the second mixer 148. The dutyperformed by the first and third mixers is to homogeneously mixcomponents derived from separate incoming streams whereas the dutyperformed by the second mixer is to create a dispersion of thepolymerizable liquid precursor as disperse phase in the dispersionmedium as continuous phase.

Gradual heating of the polymereizable liquid precursor either before orafter formation of the combined stream with the liquid suspension mediumis not desirable because increase in viscosity and agglomeration ofpolymerised material are difficult to avoid. The combined streamentering the mixer 148 is desirably at a temperature as close aspossible to that of the designed polymerization temperature for column152 but limited by the rate at which the combined stream polymerizes. Insome embodiments it is preferably not more than 120° C. as fixed by thepolymerization rate of the combined stream. The height of the column 152is in practical embodiments considerable e.g. about 6 meters, and theskilled designer will wish to make it no higher than is necessary toenable polymerization of descending beads to reach completion or atleast for the beads to have become hardened against agglomeration by thetime that they leave the column. Although the column 152 is heated, thatis primarily to maintain the polymerization temperature within thecolumn rather than to heat the dispersion entering the column to thedesigned polymerization temperature. In embodiments the designedtemperature of the column 152 is 150° C., the dispersion medium leavingheat exchanger 144 is designed to be at that temperature, and thetemperature of the streams 114, 122 combining and entering mixer 128 isdesigned to be approximately 120° C. as defined by the reactivity of themixed feed stream. The designer may have an incentive to keep mixer 128relatively cool to minimize polymerization problems within it. However,the extent to which this is feasible in some embodiments is limited bythe need not to unduly cool the stream entering mixer 148 andpolymerization column 152. The stream 126 cools the material in stream142 with which it becomes combined, but only to a limited extent becausethe flow rate in stream 142 is a multiple of that in stream 126. Thecombined stream entering mixer 148 already contains precursor that hasbegan to polymerize rapidly because it is already at or close to thedesigned polymerization temperature, and it will be appreciated thatthis places severe constraints on the time that for which the stream canbe resident in mixer 148 and within which dispersion can be completed.

It has been found that both the mixing and the dispersion duties can beperformed using in-line static mixers. They have no moving parts, arepowered by pressure difference and operate by radial transport of fluidstreams passing through them and by dividing the fluid streams intomultiple partial streams which are then recombined. Such mixers may bebased on a tubular casing having two or more grids of elements arrangedat angles to the longitudinal axis of the casing and to each other sothat each intersects the other, the grids optionally being configured inrelatively short axial sections each defining a mixing stage anddiffering from adjacent sections e.g. in rotational position of themixing elements and/or in configuration of the mixing elements, seeGB-A-2061746 (Streiff, Sulzer) and US 2004/0125691 (Streiff et al.), thedisclosures of which are incorporated herein by reference. More detailson in-line static mixers may be found in Sulzer Technical Review,3/1977, 108-113 and Streiff et al., Recents Progres en Genie deProcedes, 11, 307-314 (1997), the disclosures of which are alsoincorporated herein by reference. They are significantly better thanmixing valves, orifices or perforated plates which are well-known forproducing dispersions but which have the disadvantages of unduly widedroplet size distribution and poor efficiency. In-line static mixerstypically have an open area of more than 50% e.g. more than 70%, whichsignificantly reduces the likelihood of material agglomerating withinthem and leading to blockage. Further information about a four-elementKosch-Glitsch XMX static mixer is given by J. M. Zalc et al., PolymerEngineering and Science, 43, No 4, 75-889, the disclosure of which isincorporated herein by reference.

It will be appreciated that these mixers are of complex internalconstruction and flow pattern, and that it may not always be appropriateto use simple descriptions such as laminar or turbulent to describe theflow regimes within them, especially as such flow regimes will beaffected by the flow rates at which the mixers are operated. Somemanufacturers regard flows through in-line static mixers with Reynoldsnumbers <200 as being laminar, 200-500 as being transition laminar,500-2100 as transition turbulent and >2100 as being turbulent. Whendispersing one liquid in another, Reynolds number has implications fordroplet size because it measures the scale within a liquid ormulti-liquid steam where viscous forces become comparable to inertialforces and provides an indication of the size of the smallest eddiesthat can exist in a stream and hence the size of the droplets likely tobe formed in the stream.

FIG. 4 shows the active elements of a mixer of this type. The mixingelement 80 comprises mixing bars 82, 84 grouped together in grids of, inthis instance, four parallel bars, each grid being angled relative tothe longitudinal axis of the mixer and with the bars interfitting andintersecting as shown. Pairs of intersecting bars occur in relativelyshort longitudinal groups 86, 88, 90 with the groups being rotatedrelative to adjacent groups e.g. at 90°. The mixing element 80 fits intoa casing, a short length of which appears at 92, but which is elsewherecut-away to reveal the mixing element. The fluid is split intoindividual streams in the open intersecting channels of each mixingelement, and at each intersection a part of the flow is sheared off intothe crossing channel. In this way, inhomogenities are evened out twodimensionally in the first element and three-dimensionally in the secondelement. In the case of a mixer acting as a disperser the thin plates ofthe mixing element first subdivide the flow. When a drop passes into theinterfacial area of the intersecting channels, it is subjected todynamic pressure variations owing to the velocity components beingdisplaced through 90°, and becomes deformed as a result. If its diameterexceeds a critical value, the drop breaks up.

With reference to the static mixer 148 that disperses the polymerizableliquid precursor in the dispersion medium, for a given set of fluidphysical properties, the main influence on the drop size produced by astatic mixer is the specific energy dissipation rate, which is in turncontrolled by the mixer geometry and fluid velocity.

$\begin{matrix}{\mspace{79mu} {{{Pressure}\mspace{14mu} {drop}} = {{\Delta \; P} = {\frac{\rho \; u^{2}}{2}f_{D}\frac{L}{D}}}}} & {{Equation}\mspace{20mu} 1} \\{{{Specific}\mspace{14mu} {energy}\mspace{14mu} {dissipation}\mspace{14mu} {rate}\mspace{14mu} ɛ} = {\frac{Q\; \Delta \; P}{M} = {{\frac{\pi \; D^{2}}{4}u\frac{\rho \; u^{2}}{2}f_{D}\frac{L}{D}\frac{4}{\pi \; D^{2}L\; \rho}} = \frac{u^{3}f_{D}}{2D}}}} & {{Equation}\mspace{20mu} 2}\end{matrix}$

where

D pipe diameter m f_(D) Darcy friction factor — L mixer length m M masskg P pressure Pa Q volumetric flowrate m³ s⁻¹ u velocity m s⁻¹ ε energydissipation rate W · kg⁻¹

The dissipation rate calculated is an average over the whole mixer,although there will be local variations within the mixer with the peakrate perhaps ten times the minimum. This is considerably more uniformthan a stirred tank, where the peak dissipation rate may be manyhundreds of times higher than the minimum. However, this non-uniformityof energy dissipation means that the mixer has to be long enough toensure that all the dispersed phase fluid has passed through regions ofhigh dissipation for the desired drop size to be reached.

According to a more developed theory by Streiff et al., 1997, supra, theturbulent dispersion process is governed by the ratio of the stressforces outside the particle to the surface forces inside the drop. Thisratio is controlled by the Weber number, We. This ratio must exceed acritical value for drop break up to occur. For the largest stable dropwith a diameter d_(max), We=We_(c) The stress forces are created byturbulent eddies of size l_(e)=0.1/D_(h) where P_(h) is the mixerhydraulic diameter—in the case of the second embodiment—˜1.5 mm.microscale of turbulence. Drops with a size of l_(k) are then simplytransported with these eddies and do not undergo any further break upwhere:—

l _(k)=(v _(c) ³/ε)^(0.25)  (3)

where v_(c) is the continuous phase kinematic viscosity. As such l_(k)is the smallest drop size than can be created. In one embodiment this isin the range of 40-60 microns.

Drops therefore break, according to this model if:—

l_(k)<d_(max)<l_(e)  (4)

The specific energy dissipation, ε, is a function of the mixer designand the flow velocity and is given by:—

$\begin{matrix}{ɛ = {\frac{f \cdot V_{s}^{3}}{2 \cdot \theta^{3} \cdot D_{h}} = \frac{{Ne} \cdot V_{s}^{3}}{\theta \cdot D_{t}}}} & (5)\end{matrix}$

where f is the friction factor, V_(s) is the superficial liquid velocity(m/s), θ is the mixer void fraction, Ne is the Newton number and D_(t)is the mixer tube diameter. For operating conditions in one embodimentthis provides for a minimum bead size of between 20 and 40 microns.

The distribution of energy dissipation within a mixer is a function oflocal velocity variations created by the turbulence. This is not uniformand therefore the drop sizes vary. However in a static mixer points oflower and higher energy dissipation are regularly distributed and allthe flow passes through these regions. Accordingly, the energydistribution and the resulting bead size distribution should be far moreuniform that in a stirred tank or a dynamic in-line mixer provided thatthe mixer length is sufficient. The nature of the inline mixers is suchthat fully developed turbulence and mixing occurs at much lower Reynoldsnumbers than in empty tubes or stirred tanks, typically for an SMV mixerat Re_(Dh)>200 (Reynolds number calculated based on the hydraulicdiameter). Studies have shown that in an SMV mixer a homogeneous energydistribution is achieved in a large part of the mixer volume forRe_(Dh)˜30000 which is significantly higher than achieved in the currentL2 trials. Under these circumstances Hinze demonstrated that the largeststable drop size in isotropic turbulent flow was given by:—

$\begin{matrix}{d_{\max} = {\left( \frac{{We}_{c}}{2} \right)^{0.6}\left( \frac{\sigma}{\rho_{c}} \right)^{0.6}ɛ^{- 0.4}}} & (6)\end{matrix}$

where σ is the interfacial tension and ρ_(c) is the continuous phasedensity. The main problem with applying this theory is that We_(c) is afunction of d_(max) which precludes direct calculation of d_(max):—

${We}_{c} = \frac{\rho_{c}V^{2}d_{\max}}{\sigma}$

In addition the mixer length and flow velocity were varied. The basisfor the evaluation was that the theory was more specifically related tothe maximum stable drop size rather than d_(sv), the Salter meandiameter. This equation was subsequently modified to allow forvariations in the density between the continuous and dispersed phase(specifically for gas-liquid systems where the variation is significantalthough it is now also used for liquid-liquid systems)

$\begin{matrix}{d_{\max} = {\left( \frac{{We}_{c}}{2} \right)^{0.6}\left( \frac{\sigma}{\rho_{c}} \right)^{0.6}\left( \frac{\rho_{c}}{\rho_{d}} \right)^{0.2}ɛ^{- 0.4}}} & (7)\end{matrix}$

Calabrese then showed that the viscosity of the drop can also influencethe dispersion process as We_(c) is only directly applicable to a lowviscosity disperse phase. The liquid within the drop is in circulationdue to the external pressure distribution that gives rise to internalsheer forces that tend to stabilise the drop and reduce drop break up.This lead to the introduction of a viscosity number Vi that modifies thecritical Weber number:—

We _(c) ^(#) =We _(c)((1+B·Vi)

where:—

$\begin{matrix}{{Vi} = {\left\lbrack \frac{{\eta_{d}\left( {ɛ \cdot d_{\max}} \right)}^{0.33}}{\sigma} \right\rbrack \left( \frac{\rho_{c}}{\rho_{d}} \right)^{0.5}}} & (8)\end{matrix}$

This leads to an equation for d_(max)

$\begin{matrix}{d_{\max} = {{C_{n}\left( \frac{\left( {1 + {BV}_{i}} \right){We}_{c}}{2} \right)}^{0.6}\left( \frac{\sigma}{\rho_{c}} \right)^{0.6}\left( \frac{\rho_{c}}{\rho_{d}} \right)^{0.1}ɛ^{- 0.4}}} & (9)\end{matrix}$

These drop size equations are however only valid for dilute dispersephase systems where coalescence does not occur. If the disperse phasefraction is higher it tends to dampen the turbulence in the continuousphase and leads to larger drop sizes. This is given by:—

d(φ_(d))=(1+kφ _(d))d  (10)

where φd is the disperse phase fraction. Based on a theoreticalevaluation Doulah found that k=3 although wide variations have beenfound in practical studies. The resulting drop size is also anequilibrium between dispersion and coalescence. In regions of lowturbulence the drop size increases whilst the smaller drop sizes can bestabilised by dispersants. The overall effect of coalescence anddisperse phase fraction cannot be predicted exactly although (9) givesthe form of the relationship. This then gives the overall form of therelationship shown in (11);

$\begin{matrix}{{d\left( \phi_{d} \right)} = {{C_{n}\left( {1 + {k\; \phi_{d}}} \right)}\left( \frac{\left( {1 + {BV}_{i}} \right){We}_{c}}{2} \right)^{0.6}\left( \frac{\sigma}{\rho_{c}} \right)^{0.6}\left( \frac{\rho_{c}}{\rho_{d}} \right)^{0.1}ɛ^{- 0.4}}} & (11)\end{matrix}$

The constant, C_(n), in equation (11) provides the means for relatingthe maximum particle size to the drop size distribution. These arecharacterized by d₁₀, d₅₀, d_(sv), d₉₀ and d_(max) where d_(max) can beapproximated by d₉₉. This means that 10%, 50% etc of the drop swarm isin particles of less than the associated drop size. C_(n) depends on themixer design and the operating conditions.

This approach again predicted that the mean bead particle size wasprimarily a function of the interfacial tension between the oil and theresin phases and the linear velocity through the inline mixer but nowalso brought in the disperse phase properties, which is the main changefrom the initial approach. The underlying principle did now howeverallow for the production of smaller beads during the bead break upprocess.

The mixer 128 for mixing the first and second components streams of theliquid precursor was a Sulzer SMXS mixer, in which the mixing elementsare bars. The mixer 146 for homogenizing the inlet oil flow was a SulzerSMV mixer in which the crossing elements were corrugated plates, but wasotherwise generally similar to that shown in FIG. 4. The mixer 148 fordispersing the reaction mixture in the oil was a five element SulzerSMXL mixer in which the crossing elements were also bars arrangedgenerally similarly to FIG. 4.

In the embodiment of FIG. 4 the stream 114 was of a small moleculecross-linker in a small molecule polar organic solvent and was ofviscosity about 3 cP (relatively low, comparable to a flowable liquidsuch as water) whereas the stream 122 was of a cross-linkable oligomerin the same polar solvent and was of viscosity about 350 cP (comparableto high viscosity motor oil, SAE 40) to give a combined stream ofviscosity about 75 cP (comparable to lower viscosity motor oil, SAE 10).A Sulzer SMXS mixer was used as mixer 128 for handling relativelyviscous materials and was configured to operate in generally laminarflow conditions. It had a diameter of 6 mm and length 8 cm, was requiredto handle a maximum flow of about 10 ml/sec at a linear through-flowspeed of about 35 cm/sec and at a Reynolds number of 12. These maximumflow conditions corresponded to a pressure drop of about 1 bar acrossmixer 128 and a residence time of the material flowing through of about0.2 seconds. In a practical run, the flow rate was 2.5 ml/sec (10kg/hour) at a linear velocity of about 9 cm/sec and at a Reynolds numberof 4 and at a residence time of about 0.8 sec. The material was >30° C.below the intended polymerization temperature (the temperature beingselected to ensure that the extent of reaction in mixer 128 wasminimized while limiting the temperature decrease of the mixed feedentering the mixer 148) so that its rate of polymerization wasrelatively low and its residence time under these conditions was suchthat insignificant polymerization took place within mixer 148. Suchpolymerization will first become apparent by an increase in viscosity inthe stream flowing through the mixer.

The mixer 146 had the duties of firstly mixing a main stream 134 ofdispersion medium and a minor stream 140 of dispersant in dispersionmedium and secondly smoothing out any thermal irregularities followingpassage through heat exchanger 144 where the dispersion medium is heatedto or close to polymerization temperature. The maximum designed flow ofheated dispersion medium through mixer 146 was about 32 ml/sec (118litres/hour), i.e. more than three times the maximum designed volumeflow rate of the liquid precursor, at a linear through-flow speed ofabout 40 cm/sec. Mixer 146 was of diameter 6 mm and length 8 cm, and wasof the Sulzer SMV type configured for turbulent mixing with high masstransfer rate. The heated dispersion medium had a viscosity of only 0.5cP, and the mixer 146 was designed to operate at a Reynolds number ofabout 1700 at the maximum designed flow rate which is considered to bewithin a turbulent transition region, with a pressure drop at maximumflow of only about 0.01 bar. Residence time within the mixer at thatflow rate was about 0.2 sec. In a practical experiment the dispersionmedium was passed through the mixer 146 at a rate of about 16 ml/sec (50kg/hour) corresponding to a speed through the mixer of about 20 cm/sec,a residence time of about 0.4 sec and a Reynolds number of 850, althoughstill within the transition turbulent flow region. It will be noted thatthe weight ratio of the feeds in the precursor and dispersion mediumstreams was about 5:1, i.e. the dispersion medium is in substantialexcess (e.g. in some embodiments >3:1 and in some embodiments within arange 3:1 to 10:1).

The mixer 148 had the duty of dispersing the polymerizable liquidprecursor in the liquid dispersion medium. It was a Sulzer SMXL mixer ofdiameter 10 mm and length 33 mm. The combined stream flows through at amaximum design rate of 42 ml/sec and at a corresponding velocity ofabout 57 cm/sec giving a corresponding minimum designed residence timeof about 0.6 sec and a Reynolds number of about 4600, which is well intothe turbulent flow regime. In a practical embodiment, the combinedstream flowed through mixer 148 at 18.5 ml/sec corresponding to a linearspeed of about 25 cm/sec, a Reynolds number of about 2000 (close totransition to fully turbulent flow) and a residence time of about 1.8sec. This is insufficient for polymerization to have proceededsubstantially within mixer 148, notwithstanding that the stream passingthrough it is at or close to the designed polymerization temperaturewithin polymerization column 152. Again, undue polymerization withinmixer 148 will be first observed by an increase in viscosity of thematerials passing through it, and a corresponding increase in dropletsize from its intended value. Treatment of the combined stream so as todisperse the polymerizable liquid precursor as droplets in thesuspension medium is in some embodiments completed within 0.5-5 secs,e.g. 1-3 secs, more preferably in some embodiments 1.5-2 secs.

Preferably there is used a mixer 148 capable of dispersing thepolymerizable resin precursor in the dispersion medium so as to allowthe formation of solid particles having a mean particle size of up to1500 μm, i.e. which permits production of large size beads. For somepurposes the operating conditions may be that the average bead size maybe higher than this. For example, the operating conditions may be thatthe mean droplet and hence bead size is up to 2000 μm. In a preferredaspect, the mixer may be used to generate solid particles having a meanparticle size of from 100 μm to 1500 μm, preferably from 300 μm to 1000μm.

It is preferred that the polymerizable precursor is dispersed in thedispersion medium to produce droplets having a relatively narrowparticle size distribution so as to produce resin beads that have asimilar relatively narrow particle size distribution. Any sample ofparticulate material will have a statistical distribution of particlesizes about a mean value. The ratio of the 90^(th) percentile (D90) tothe 10^(th) percentile (D10) gives a measure (D90/D10) of the spread ofthe distribution of particle size in the sample. The droplets and curedresin beads that may be produced according to the present processpreferably have a D90/D10 particle size distribution that is nor morethan 10, desirably not more than 5, and advantageously about 2. By wayof comparison, for coconut charcoal the mean particle size willtypically be in the range 100-1000 μm, with a D90/D10 ratio of 20 ormore, a significant proportion of the particles being less than 20 μm insize.

The mixer 148, in the embodiment discussed above, has the duty ofdispersing a viscous stream of polymerizable liquid precursor e.g.consequent on the presence of oligomers therein (e.g. viscosity >20 cP,e.g. in some embodiments >50 CP) as droplets in a free-flowing stream ofdispersion medium (viscosity <2 cP, e.g. in some embodiments <1 cP).This duty has to be completed in the limited residence time in thein-line static mixer which is available before polymerization proceedstoo far, and beads of a desired size and desired size distribution haveto be produced. As is apparent, the inventors have discovered that theseduties can be performed by in-line static mixers and the necessaryresults can be achieved.

Polymerization Stage

The following conditions are specific to the novolak/hexamine system.The mixed and dispersed liquid precursor mixed and dispersed in thesuspension medium is passed direct from the mixer 148 to a region 150,152 where the flow of dispersion medium becomes laminar andpolymerization proceeds rapidly e.g. within a period of 30 seconds to 5minutes e.g. 1-4 minutes giving hardened beads which can be recoveredfrom the dispersion medium without aggregation and without significantdeposition of aggregated material during the polymerization process. Insome embodiments, the droplets of reaction mixture are allowed toundergo polymerization in a descending column 152 of the dispersionmedium under conditions such that the droplets neither aggregate norbreak up and the reaction mixture becomes fully cured to resin by thetime it reaches the base of the column so that the resulting beads ofresin can be collected and recovered without them aggregating.

For example, in a novolac/hexamine/ethylene glycol system, ethyleneglycol which is preferably used as solvent and pore former has a densityof 1.1 at room temperature, boils at 197.3° C. at ambient pressure andis immiscible with aliphatic hydrocarbons e.g. transformer oil or othermineral oil used as dispersion medium. As regards reactants, phenolmelts at 40.5° C., boils at ambient pressure at 181.7° C. and has adensity of 1.07. Paraformaldehyde melts at 120° C. and has a density of1.45. Industrial novolac resins are typically of density 1.1 or abovedepending upon molecular weight. Hexamine (hexamethylene tetramine) hasa density of 1.3, melts at 238-244° C. and is stated to boil at ambientpressure at 270° C. but decomposes to give reactive cross-linkingcomponents at ˜120° C., i.e. below the temperature of the mixedreactant/dispersant stream. Cured resin based on phenol and formaldehydehas a density of about 1.1. The density of the starting materials and ofthe beads of cured resin formed are greater throughout the course of thecuring reaction than the density of the mineral oil in which they aredispersed.

It follows that mineral oil can be handled easily at the temperaturesneeded to effect polymerization which may be up to 160° C., e.g. about150° C., and that the physical properties of the reactants are such thatthey can in principle be maintained in dispersion at the requiredpolymerization temperature. If the mineral oil is employed as agradually descending column 152 with non-turbulent flow, then disperseddroplets of reaction mixture will fall under gravity through the oil andwill descend at a speed greater than the speed of descent of the oil.The speed of descent of the dispersed droplets will depend on dropletsize and the viscosity of the oil, but their average speed of descentmay be at least twice the speed of descent of the oil e.g. 5-20 timesthe speed of descent of the oil. For example the column 152 may be ofheight 5-10 metres e.g. about 6 metres, and the speed of the oil may besuch that on average it will descend the length of the column in about30-60 minutes. It will be appreciated that the dispersed reactionmixture forms a population of droplets having different sizes, and thatthe largest droplets will descend the more rapidly. The conditions e.g.of oil viscosity and column height are desirably such that the largestdroplets become cured during their descent down the column and thatuncured droplets do not reach a receiving vessel at the base of thecolumn where if incompletely cured they might adhere together and formobjectionable aggregates. The speed of descent of the droplets may, forexample, be such that they will descend the length of the column in morethan 2 minutes e.g. about 4-5 minutes which is a sufficient time for thepolymerization reaction to reach completion.

It has been found that droplets of reaction mixture can be cured in sucha column in a residence time of 30 seconds-5 minutes, e.g. 1-4 minutes,more preferably 2-4 minutes with development of good mesoporosity in theresulting resin which remains apparent in carbonized materialsubsequently derived from the resin.

Resins and their Utility in Forming Carbonized Materials

The invention is applicable to the formation of polymerized beads fromany polymerizable liquid reaction mixture that can be dispersed into animmiscible liquid dispersion medium and hardened or cured as dropletswhilst in suspension in or travelling through a laminar flow of saidmedium. It is applicable to reaction mixtures as aforesaid that containa pore former in an amount effective to impart mesoporosity to beadsformed from the dispersed droplets by polymerization.

It is applicable to the production of resin beads useful inter alia asintermediates in the production of beads of carbonized material and alsoe.g. as ion-exchange materials. Examples of carbonizable organic resinsthat can be converted to carbon materials include hydroxyl-substitutedaromatic resins and non-phenolic resins such as those derived fromstyrene and vinyl pyrolidone or from styrene and divinyl benzene.Hydroxy-substituted aromatic resins are preferred, especially thosederived from phenols.

The invention specifically includes a process for producing a porouscarbon material comprising the steps of condensing a nucleophiliccomponent with an electrophilic cross linking agent in the presence of apore former to form a resin, carbonising the resin and activating theresulting carbon material.

Phenolic Resins—Nucleophilic Component

The present resins can be prepared from any of the starting materialsdisclosed in WO 02/12380. Nucleophilic components may comprise phenol,bisphenol A, alkyl phenols e.g. cresol, diphenols e.g. resorcinol andhydroquinione and aminophenols e.g. m-amino-phenol.

It is preferred to use as nucleophilic component a novolac or otheroligomeric starting material which because it is already partlypolymerized makes the polymerization to the desired resin beads a lessexothermic and hence more controllable reaction. The preferred novolacshave weight-average molecular weights (Mw) in the range of from 300 to3000 prior to cross-linking (corresponding to a DP with respect tophenol of about 3-30). Where novolac resins are used, they are solidswith melting points in the region of 100° C. Novolac resins of Mw lessthan 2000 and preferably less than 1500 form resins which, oncarbonisation, tend to produce carbons with desired pore sizedistributions using lower amounts of pore former. Whilst commercialnovolacs are largely produced using phenol and formaldehyde, a varietyof modifying reagents can be used at the pre-polymer formation stage tointroduce a range of different oxygen and nitrogen functionalities andcross-linking sites. These include but are not limited to:—

(a) Diphenols e.g. resorcinol and quinines e.g. hydroquinone. Both aremore reactive than phenol and can lead to some cross-linking at thepre-polymer production stage. It is also possible to introduce thesecompounds at the cross-linking stage to provide different cross-linkingpaths. These also increase the oxygen functionality of the resins.

(b) Nitrogen containing compounds that are active in polycondensationreactions, such as urea, aromatic (aniline, m-amino phenol) andheteroaromatic (melamine) amines. These allow the introduction ofspecific types of nitrogen functionality into the initial polymer andfinal carbon and influence the development of the mesoporous structureof both the resins and the final carbons. Like hydroquinone andresorcinol, all the nitrogen containing nucleophilic modifying reagentswhich can be used possess two or more active sites and are more reactivein condensation reactions than phenol or novolacs. It means that theyare first to react with primary cross-linking agents forming secondarycross-linking agents in situ.

Novolacs are thermally stable in that they can be heated and cooledrepeatedly without structural change. They are cured on addition ofcross-linking agents and heating.

The nucleophilic component may be provided alone or in association witha polymerization catalyst which may be a weak organic acid miscible withthe novolac and/or soluble in the pore former e.g. salicylic acid,oxalic acid, phthalic acid or p-toluenesulfonic acid (but preferably notfor resins intended to be carbonized as the addition ofsulphur-containing compounds is undesirable). The salicylic acid assupplied is 1.5%, and if desired the amount may be increased to 2.5% orbeyond.

The concentration of novolac in the pore former is such that whencombined with the solution of cross-linking agent in the same poreformer the overall weight ratio of pore former to (novolak+crosslinkingagent) is at least 125:100 by weight. The actual ratios of novolak:poreformer and crosslinking agent:pore former are set by the operation ofthe plant and are controlled by the viscosity of the novolac:pore formersolution such that it remains pumpable and the ratio of crosslinkingagent:pore former such that the crosslinking agent remains in solutionthroughout the plant.

Cross-Linking Agents for Phenolic Resins

The cross-linking agent is normally used in an amount of from 5 to 40parts by weight (pbw) per 100 parts by weight of the nucleophiliccomponents e.g. novolac, typically from 10 to 30 (e.g. 10, 15 or 20) pbwcross-linking agent per 100 pbw of nucleophilic component. It may be,for example, an aldehyde e.g. formaldehyde or furfural or a polyaminee.g. hexamethylenetetramine (hexamine), melamine or hydroxymethylatedmelamine.

Hexamine is preferably used for cross-linking novolac resin at aconcentration of 10 to 25 e.g. about 20 pbw hexamine per 100 pbw ofNovolac. This ensures formation of the solid resin with maximalcross-linking degree and ensures the stability of the mesopore structureduring subsequent removal of the pore former. This is in contrast topreviously disclosed sintered resin structures which typically requireup to 3 pbw of hexamine per 100 pbw of novolac.

Pore-Formers

The pore former also acts as solvent. Thus, the pore former ispreferably used in sufficient quantities to dissolve the components ofthe resin system, the weight ratio of pore former to the totalcomponents of the resin system resin being preferably at least 1.25:1.It preferably comprises a polar organic liquid chosen in combinationwith the dispersant which is a non-polar organic liquid so as to form amainly or wholly immiscible combination, the greater the incompatibilitybetween the pore former which forms the dispersed phase and thedispersion medium, the less pore former becomes extracted into thedispersion medium. The pore former desirably has a greater density thanthe dispersion medium with which it is intended to be used so thatdroplets of the pore former containing dissolved resin-formingcomponents will pass down a column more rapidly than a descending flowof dispersion medium therein. Both protic and aprotic solvents ofdifferent classes of organic compounds match these requirements and canbe used as pore formers, both individually and in mixtures. In additionto dissolving the reactive components and any catalyst, the pore formershould also, in the case of phenolic resins, be compatible with waterwhich is formed by elimination as polymerization proceeds, and the poreformer is preferably highly miscible with water so that it can bereadily removed from the polymerized resin beads by washing.

Details of suitable pore formers are given in WO 02/12380 A2 (Tennison).The pore former may be, for example, a diol, a diol-ether, a cyclicester, a substituted cyclic or linear amide or an amino alcohol e.g.ethylene glycol, 1,4-butylene glycol, diethylene glycol, triethyleneglycol, γ-butyrolactone, propylene carbonate, dimethylformamide,N-methyl-2-pyrrolidinone and monoethanolamine, ethylene glycol beingpreferred, and where the selection is also limited by the thermalproperties of the solvent as it should not boil or have an excessivevapour pressure at the temperatures used in the mixer or curing column.

It is thought that the mechanism of mesopore generation is due to aphase separation process that occurs during the cross-linking reaction.In the absence of a pore former, as the linear chains of pre-polymerundergo cross-linking, their molecular weight initially increases.Residual low molecular weight components become insoluble in the highermolecular weight regions causing a phase separation into cross-linkedhigh molecular weight domains within the lower molecular weightcontinuous phase. Further condensation of light components to theoutside of the growing domains occurs until the cross-linked phasebecomes essentially continuous with residual lighter pre-polymer trappedbetween the domains. In the presence of a low level of pore former thepore former is compatible with, and remains within, the cross-linkedresin domains, (e.g., <120 parts/100 parts Novolac for theNovolac-Hexamine-Ethylene Glycol reaction system), whilst the remainderforms a solution with the partially cross-linked polymer between thedomains. In the presence of higher levels of pore former, which exceedthe capacity of the cross-linked resin, the pore former adds to thelight polymer fraction increasing the volume of material in the voidsbetween the domains that gives rise to the mesoporosity. In general, thehigher the pore former content, the wider the micropores and the higherthe pore volume.

This phase separation mechanism provides a variety of ways ofcontrolling the pore development in the cross-linked resin structures.These include chemical composition and concentration of the pore former;chemical composition and quantity of the cross-linking electrophilicagents, presence, chemical nature and concentration of modifyingnucleophilic agents, chemical composition of phenolic nucleophiliccomponents (phenol, novolac), presence, chemical nature (acidic, basic),the presence of water within the solvent and concentration of any curingcatalyst if presentt.

Dispersion Medium

The dispersion medium is a liquid which can be heated to the temperatureat which curing is carried out e.g. to 160° C. without boiling atambient pressure and without decomposition and which is immiscible withethylene glycol and with the dissolved components therein. It may behydrocarbon-based transformer oil which is a refined mineral oil and isa by-product of the distillation of petroleum. It may be composedprincipally of C₁₅-C₄₀ alkanes and cycloalkanes, have a density of0.8-0.9 depending upon grade and have a boiling point at ambientpressure of 260-330° C., also depending upon grade. Transformer oil hasa viscosity of about 0.5 poise at 150° C. which is a typical curetemperature. As previously explained, transformer oil or otherdispersion medium is typically used in volumes 3-10 times the volume ofthe combined streams of nucleophilic precursor and crosslinking agente.g. about 5 times.

Dispersing Agents

Preferred dispersing agents which are dispersed in the dispersion mediumbefore that medium is contacted with the reaction mixture to bedispersed therein to retard droplet coalescence are either sold asdrying oils e.g. Danish oil or are produced by partially oxidizingnaturally occurring precursors such as tung oil, linseed oil etc. Thedispersing agents are consumed as the process proceeds, so that if thedispersion medium is recycled, dispersing agent in the recycled oilstream should be replenished. The dispersing agent is convenientlysupplied as a stream in solution in the dispersion medium e.g.transformer oil and e.g. in an amount of 5-10% v/v where Danish oil isused which contains a low concentration of the active component. Moresolution would be used of the oxidised oils.

An embodiment uses a version of Danish Oil as the dispersant which is aproprietary wood treatment/varnish that comprises Tung oil dispersed inkerosene with curing agents (siccatives) such as cobalt ethyl hexanoateand other unidentified resin components. It is preferred that thereshould be present a naturally occurring oil that has been oxidized to acontrolled extent. Controllable dispersion performance has been achievedwith Tung oil and linseed, both conventional drying oils, and food gradeoils such as soya, sunflower and rapeseed, the latter simply requiringmore severe oxidation conditions to render them effective e.g rapeseedoil may require 3 or more days for optimal performance

Preferred Combination of Resin-Forming Materials

The preferred resins for use in producing porous carbon materials arenovolak resins cross-linked with hexamethylene tetramine (hexamine) inethylene glycol as pore forming agent with Danish oil as dispersant intransformer oil as dispersion medium.

Preferred Apparatus and its Use

In a second embodiment of the apparatus of FIG. 1, a feed tank or vessel10 for one component of the polymerizable liquid precursor e.g. hexaminein ethylene glycol was provided with stirrer 12. Hexamine/ethyleneglycol solution was formulated on site by adding solid hexamine,supplied by Plater Chemicals, to ethylene glycol in the vessel 10 andstirring until the hexamine dissolved. The vessel was pressurised e.g.to about 3 bar and was maintained originally at 90° C. by an externalsteam jacket, but this was increased to 110° C. after an initial run.The first component passed from the tank 10 via flow control valve 16through line 14 which was not heated. Initially the feed tank 10 waspressurized to the required level and then left, leading to a slowdepressurization as the tank emptied. Pressure forced flow was used inpreference to a pump to avoid any pulsations in the flow that might haveimpacted on the performance of in-line mixers 28, 48 located downstream.A feed tank 18 for a second component of the polymerizable liquidprecursor e.g. novolac in ethylene glycol was provided with stirrer 20,was pressurised to about 3 bar to provide pressure forced flow and wasalso maintained originally at 90° C. by an external steam jacket.

In use, novolac was supplied as a 65% w/v solution of TPR210 resin inethylene glycol by Hexion Ltd in 1 m³ stainless steel steam heatedIBC's. The TPR210 contained 1.5% free salicyclic acid which serves ascuring catalyst. There was purchased 20 m³, representing a singleproduction batch. Vessel 18 was replenished with this feed as requiredThis component passed from the tank 18 via line 22 in which there was asecond flow control valve 24. The line 22 was electrically trace heatedto 80° C. for part of its length to prevent the novolac from setting inthe line. The second component comprising hexamine dissolved in ethyleneglycol was prepared in vessel 10 by dissolving solid hexamine in theethylene glycol at a concentration sufficient to give the requiredresin:solvent ratio in the combines dtream. This component passed fromvessel 10 via line 14 through control valve 16. This line was heated to˜80° C. to prevent hexamine recrystallizing. The volumes of vessels 10,18 were 7 m³ and approximately 5 m³ of each feed was prepared. The twoflows 14, 22 were independently controlled using hand control valves 16,24 via mass flow meters, were combined in line 26 and were supplied tofirst in-line mixer 28 where they were intimately mixed under turbulentflow conditions to form the polymerizable liquid precursor.

Transformer oil to provide a continuous phase into which thepolymerizable liquid precursor was to be dispersed was stored in supplytank 30 with stirrer 32, again under a pressure of about 3 bar forpressure forced flow, and passed through line 34. A small flow ofdispersant e.g. 8% v/v Danish oil in transformer oil from feed tank 36was supplied continuously by pump 38 via line 40 to the transformer oilin line 34. The dispersant was consumed during the polymerizationreaction, and therefore had to be replenished as the transformer oil wasrecirculated. The combined flow of transformer oil and dispersant flowedthrough line 42 to a tubular pre-heater 44 where it was heated to ˜145°C. and then to in-line mixer 46 where the dispersant and the transformeroil mixed under turbulent flow conditions.

The streams of polymerizable liquid precursor and transformeroil/dispersant were combined and fed to main mixer assembly 46, 48 via asparged injector that comprised initial a 1 cm pipe with 4×2 mm holes.Recycled hot oil entered upper in-line mixer 46 that ensured that theoil and dispersant were thoroughly mixed. The resulting stream, e.g. ata flow rate in the range from 600 to 1000 L/hour, was combined with themixed feed stream, e.g. at a flow rate in total of between 100 and 200L/hour. The combined stream passed to main bead dispersion mixer 48which was a “dip leg” mixer 48 partially immersed in the hot oil at therelatively large diameter head region 50 of polymerization column 52.The in-line mixer 48 dispersed the polymerizable liquid precursor asdroplets of size about 500 μm and had the property that it created apopulation of droplets having a relatively narrow range of sizes. Oillevel in head region 50 was monitored by level sensor 49. The totalflow, comprising dispersed beads in the carrier oil, was then passeddown the polymerization column 52 to collection vessel 54.

When the transformer oil containing the polymerizable liquid precursorpassed from the mixer 48 into the body of oil in the head region 50 ofpolymerization column 52, its velocity decreased and turbulence waslost. It then passed in a descending flow down polymerization column 52which was of length e.g. 6 meters and was heated by a heating jacket tomaintain the material therein at a suitable polymerization temperaturee.g. 140° C. Flow of transformer oil down the column 52 was laminar. Asused herein, the term “laminar flow” refers to a flow regime in whichfluid motion is smooth and orderly, and in which adjacent layers orlaminae slip past each other with little mixing between them. Typically,a laminar flow regime exists when the Reynolds Number is below 2000.Laminar flow conditions minimized collisions between the droplets ofpolymerizable liquid precursor as they flowed down the column 52 andhence minimized aggregation of the droplets; these conditions alsominimized break-up of the droplets.

The length of the column 52 and the temperature at which it wasmaintained were configured to allow the dispersed polymerisable liquidprecursor or at least a substantial proportion thereof, to cure beforereaching the collection vessel 54 so as to minimize agglomeration of theresulting particles or beads. The column 52, shown schematically in FIG.2, had a capacity of ˜500 litres such that the oil residence time in thecolumn was around 30 minutes at 1000 L/h flow rate. In contrast,gravitational settling of the droplets or beads which, as explainedabove, were denser than the transformer oil gave a residence time for500 μn beads of about 4 minutes—i.e. the beads had a high velocity(0.025 m/s) relative to the oil flow rate (0.003 m/s) within thepolymerization column 52. This was in marked contrast to the situationwithin the in-line mixer 48 which had a free volume of around 400 ml,giving a residence time of approximately 1.5 seconds (0.4 m/s). Owing tothe short residence times within mixers 28,48 polymerization of thereaction mixture passing through them does not proceed significantly,and owing also to the flow conditions within the mixers, unintendedviscosity increases and fouling by aggregated polymerized reactionmixture were not observed. Studies indicated that at 140° C. the beadsbecame fully cured in ˜2 minutes under flash cure conditions, and it wasfound that this flash cure could be carried out whilst producing beadsof useful mesoporosity that could subsequently be converted intomesoporous/microporous carbon beads.

In use the collection vessel 54, was largely filled with oil. It wasthen pressurised to push the oil back up the column 52 so that thestatic oil head was balanced by the pressure to give a controlled levelin the head region 52 of the column as represented by the line acrossthe upper polymerization column region 50 shown in FIG. 1 and a residuallevel represented by the line across the collection vessel 54 as inFIG. 1. To further assist in controlling the levels in column 52 theinitial design comprised a “lute line” shown by the hair pin pipe 63between the recycle pump 58 and intermediate product receiving vessel62. This was intended to function like a siphon tube, maintaining thecorrect level in the head region 50 whilst oil was being pumped aroundthe circuit. It was also intended that the bead slurry pump 58 could beused to recycle the slurry from the lute line 63 back to the receivervessel to provide an enhanced linear velocity in line 63 to lift thebeads up the “lute line”.

Cured polymer beads from the column 52 passing to collection vessel 54were maintained in suspension by stirrer 56. Material from collectingvessel 54 was intended to pass via pump 58 and line 60 to first holdingvessel 62 where the beads were maintained in suspension by stirrer 64and the bead suspension was allowed to cool. In practice, however, itproved difficult to pump the bead suspension using the pump 58, andinstead pressure forced flow based on the pressure in collecting vessel54 was used instead. After cooling, material was passed fromintermediate vessel 62 to holding tank 70 where the beads weremaintained in suspension by stirrer 68 with continuous recirculation viapump 72, and the material was thence passed to centrifuge 74. Beadssubstantially free of transformer oil were passed e.g. to a storagecontainer 76 and separated oil was returned at line 78 to the vessel 30.

The column arrangement 50, 52 and collection vessel 54 are shown in moredetail in FIG. 2. Reaction mixture 25 in line 26 and transformer oil 62in line 42 passed to mixer 48 which was arranged to discharge into inthe headspace 50 which appears as a chamber which had a bottom openinginto the column 52 but was otherwise closed. Auxiliary line 65 allowedventing of gas 64 from the upper region of headspace 50. The column 52incorporated sight glasses 51, 52 and terminated in downpipe 55 whichdischarged into collection vessel 54 below the level of liquid 59 in thevessel. The headspace 57 could be purged with inert gas e.g. nitrogenfrom supply 72 via valve 74 and port 76. Pressurizing the headspace 57at start-up established the level of transformer oil in the column 52and head region 50, and the liquid level in collection vessel 54 wasdesirably maintained so that at any time by release of pressure thecolumn of transformer could return into the vessel 54.

Once removed from the product collection vessel 76, the beads werevacuum dried. Laser particle size analysis was carried out on theparticulate product. Residual levels of glycol and oil were measured bythermogravimetric analysis. The particles were examined by scanningelectron microscopy.

The particle size of vacuum dried resin samples was determined using aMalvern Masterisizer (Laser diffraction). The dry sample was fed into asmall vibrating hopper and then through a small perforated basket in anessentially fluidised state. The first part of the sample gave a“typical” result and a second part of the sample was used to ensure thatthe results were reproducible and could also be re-run to confirmreproducibility and that there was no sample attrition. The unit itselfeffectively decided when it had seen sufficient time to report theparticle size distribution, i.e. when the results had converged. Theresin sample was run as received and was not dispersed prior to testing.

Dispersion of the main particle peak size gave a D₁₀:D₉₀ ofapproximately 2.

Samples for pore structure analysis were fully vacuum dried and werethen carbonised in a single run in a large box furnace. The results aresummarised in FIG. 3 and Table 1. All of the samples show essentiallyidentical pore structure.

TABLE 1 BET Area Pore volume Bulk density Sample m²/g cc/g g/cm³ BX8 5630.66 0.55 BX10 552 0.70 0.50 BX11 553 0.70 0.54 BX12 578 0.76 0.52

A number of modifications to the embodiment described above have beenmade and successfully tested, and have already been described withreference to FIG. 5. Instead of pressure forced flow, the novolac stream114, the hexamine stream 122 and the transformer oil stream 134 arepumped from respective storage vessels 110, 118 and 130 by means of gearpumps 113, 123, 133 which have been found to be sufficiently free ofpulsation. Other forms of non-pulsating pumps may be used e.g. rotaryvane pumps or peristaltic pumps. The novolak stream and the hexaminestream may incorporate heat exchangers 115, 125 between respective gearpumps 113, 123 and the in-line mixer 128 to heat the streams enteringthat mixer e.g. to 100-120° C. or above. It is important that the streamof mixed reactants should be sufficiently warm not to unduly decreasethe temperature of the transformer oil with which it becomes mixed inthe head region 150 of the polymerization column 152, otherwise there isa risk that the required polymerization temperature in thepolymerization column 152 (which may incorporate sight glasses 151) maynot be maintained over a sufficient portion of the length of that columnand polymerization may be incomplete. The Danish oil or other dispersantmay be added to the transformer oil at the downstream side of the tubeheat exchanger 144 from a supply vessel (not shown) by gear pump 138 andline 140 in order to reduce deposition in the heat exchanger. Thereceiving vessel 154 may be operated as a settling tank with oilcontaining a sediment 153 of polymerized beads being drained from thebase of the receiving vessel 54 via drain valve 157 and pump 158 (whichmay take the form of a screw conveyor) and supernatant oil 155 from thatvessel is recycled to the oil storage vessel 130. A strainer 131 may beprovided in the return line 134 from the oil storage vessel upstream ofthe gear pump 133 therein for removing solid matter e.g. resin beadsfrom the oil being recycled and facilitating pumping by means of thegear pump. The line 159 from the receiver vessel 154 leads to a headeror overflow tank 161 which in this embodiment assists in defining theliquid level in enlarged head region 50, and has an overflow line 160providing an oil return to the oil storage tank 160. Make-up oil issupplied as required from storage vessel 170 via pump 171.

Preparing Beads for Carbonization and Activation

Beads which have been centrifuged to physically separate transformer oilas far as possible are washed in water to remove ethylene glycol andthen vacuum dried to minimise residual water and ethylene glycol.

Carbonization and Activation

A method for carbonization and activation of carbonaceous material isprovided. The method is applicable to the carbonization of carbonaceousmaterial comprises material of vegetable origin e.g. coconut-derivedmaterial. The conversion of beads of waste ion-excange resin into carbonadsorbents is disclosed inter alia by Bratek et al., Carbon, 40,2213-2220 (2001). It is also applicable to the carbonization of resinmaterials e.g. resin beads and especially phenolic resin beads. Wherethe beads have a mesoporous structure, embodiments of the method permitthe mesoporosity to be carried over into the carbonised and activatedresin beads produced. The carbonaceous material may be the product ofthe bead forming method described above.

The kiln may be provided with 5-10 weirs and the weirs may be spaced atequal intervals or at varying intervals along its length. In use, thecarbonaceous material forms a bed, portions of which are lifted andcascaded through the kiln atmosphere by longitudinally directedangularly spaced lift bars extending between weirs, the lift bars in anembodiment having a height above the internal cylindrical surface of thekiln which is approximately 50% of the height of the weirs.

The kiln preferably has an entry region configured to dry or removesolvent from the carbonaceous material, the entry region for receivingbeads preferably being maintained at not more than 350° C. andpreferably not more than 300° C. Superheated steam is preferablyintroduced at the discharge end of the kiln and flows counter-current tothe beads to provide the furnace atmosphere, the steam in an embodimentbeing introduced at about 150° C. The kiln may be configured to providea residence time for the carbonaceous material of 2-5 hours.

In an embodiment, carbonization is performed at a temperature of fromabout 600° C. to about 850° C. in a flow of non oxygen-containing gas.Activation may be performed at a temperature of greater than about 750°C., where the purge gas is steam or greater than about 800° C., wherethe purge gas is CO₂.

The kiln structure is, as previously stated provided in embodiments with5-10 weirs, and with lift bars between the weirs for agitating thecarbonaceous material, lifting portions of the material, and causinglifted material to cascade to the bottom of the kiln through the kilnatmosphere. In embodiments, a housing surrounds the body and partitionsspaced along the housing define with the body independently firedheating zones disposed along the kiln e.g. 5-10 independently firedheating zones

More specifically beads of cured resin which have been subjected to theabove mentioned washing and drying operations may be carbonized andactivated in a single operation using the rotary kiln shown in FIGS. 6and 7.

In FIG. 6, a rotary kiln generally indicated by reference numeral 200comprises an elongate open tubular kiln body 202 e.g. of mild orstainless steel of length about 3.7 metres (12 feet) and diameter about0.46 metres (18 inches) which is supported for rotation about itslongitudinal axis within thermally insulated kiln housing 204 by rollercradle assemblies 206, 208 each comprising three or more support rollershaving cylindrical surfaces that provide support for the kiln body andhave axes of rotation parallel to the axis of rotation of the kiln body.The length of 3.7 metres was selected for preliminary experiments; inorder to facilitate the carrying out of all three operations of finalsolvent evaporation, carbonization and activation, an increase in kilnlength to about 5.5 metres (18 feet) may be desirable. The rollers ofthe roller cradles may be e.g. of steel or may be of a heat-resistantplastics material e.g. phenolic plastics. Rotation may in an embodimentbe by means of a sprocket formation 210 on the outer cylindrical surfaceof kiln body 202 which is driven by motor and gearbox assembly 214through drive chain 212. High speeds of rotation are neither necessarynor desirable, and in the present embodiment where the necessarytreatment time is a few hours, e.g. about three hours, a speed ofrotation of about 1 rpm is suitable. Alternative arrangements arepossible e.g. a worm wheel formation on or attached to the outercylindrical surface of the kiln body and a worm gear driven by a motorand gearbox. The kiln body 202 is supported with its axis directeddownwardly towards a discharge end at a small acute angle e.g. about 10°to the horizontal.

An inlet chamber 216 has an opening in one of its faces which receivesthe inlet end of the kiln body 202, the chamber 216 having a seal 218which wipes the outer cylindrical surface of the body 202 to provide agas-tight seal as the body 202 is rotated. A supply hopper 220 or othersupply means supplies resin beads to be processed through the chamber216 via chute 222 to supply end region 241 a of the kiln body. Steamcarrying gas evolved by the beads during carbonization passes from thekiln body 202 into the chamber 216 and thence into discharge pipe 224 asindicated by arrow 226. Beads being processed pass along the body 202 todischarge end region 241 f and thence into discharge chamber 228 which,as in the case of chamber 216 has an opening in one of its faces whichreceives the discharge end of the kiln body and which has a seal 230which wipes the outer cylindrical surface of the body to provide agas-tight seal. Carbonized and activated beads pass into collectorfunnel 232 and thence into receiving hopper 234. Steam or otheractivation gas e.g. carbon dioxide passes through line 236 into chamber228 as indicated by arrow 238, and then passes counter-current to theflow of beads to the chamber 216 as indicated by arrows 239. It ispreferred that the atmosphere within the kiln, including the kiln body202 and inlet and discharge chambers 216, 228 is substantiallyoxygen-free. Superheated steam e.g. at about 150° C. is suitablyinjected at line 236 in an amount of 3-4 times stoichiometric based onthe amount of carbon to be removed from the carbon char during theactivation stage. The required steam flow is in practice of relativelysmall linear velocity.

The present kiln is shorter than conventional kilns and has a morepronounced downward inclination. The bead material being treated isattrition-resistant and is highly flowable compared e.g. to vegetablechar in a conventional activation furnace. For these reasons, the beadstend to flow undesirably rapidly towards the discharge end as the kilnbody is rotated, and there would be insufficient time for effective beadtreatment. This problem is avoided in the illustrated embodiment by theprovision within the kiln body 202 of annular weirs 240 a-240 e, e.g. ofsteel plate welded to the inner cylindrical surface of the body, andspaced apart along the length of the body to define bead treatmentregions 241 a-241 e and a bead discharge region 241 f downstream of thefinal annular weir 240 e. Each weir retains behind it a body 223 ofbeads to be treated, and in steady-state operation the volume of beadsin the kiln will be about 10% of the total volume of the kiln. In theembodiment of the furnace described above, the maximum bed depth, whichis immediately adjacent each weir, is about 10 cm (4 inches). Thisrelatively shallow bed depth contributes to the high speeds ofcarbonization and activation that can be achieved. Again, in theembodiment described above there were five weirs; in production kilnswhich as indicated above are longer, this may be increased e.g. to 8-10weirs, with a corresponding increase in the number of internalpartitions and heating zones in the kiln housing. In the illustratedembodiment the zones in the kiln body 241 a-241 f do not coincideprecisely with the heating zones 246 a-246 f; in other embodiments theaxial positions of weirs 240 a-240 e and the partitions 244 a-244 d maybe readjusted so that these zones do coincide so that individual controlof the temperature in each zone of the kiln body is facilitated.Movement of beads from one treatment zone to another is primarilyoverflow as additional material is supplied, this being represented bythe curved arrows 243; speed of rotation is therefore largely or whollydecoupled from bead residence time and can be selected to achievedesirable bed agitation and exposure of the bed contents to the furnaceatmosphere and without unacceptable reduction in bead residence time.Furthermore, the provision of internal weirs permits control of materialresidence time, primarily in terms of the rate of supply of freshmaterial to the kiln, whereas in a conventional kiln there is no realcontrol of residence time and the reproducibility of the carbonised oractivated material produced is poor. For example, if the total volume ofthe beads in the kiln is about 50 litres and about 10 litres/hour offresh beads is supplied from hopper 220, then the average bead residencetime in the kiln should be about 5 hours.

The thermally insulated kiln housing 204 is of shorter axial length thanthe kiln body 202 and is sealed thereto at its ends by seals (notshown). It contains annular internal partitions 244 a-244 d sealed tothe outer cylindrical surface of body by seals (not shown) to formheating chambers 246 a-246 e. The kiln is in this embodiment indirectlygas-fired. Each heating chamber contains a respective pair of gasburners 248 a-248 e and is vented at outlet 250 a-250 e, the heatsupplied to the kiln at each chamber being independently controllableaccording to need.

The internal structure of the kiln body is apparent from FIGS. 7 and 8,in which two of the weirs 240 a, 240 b appear, and between them, as inall the other zones of the kiln there are longitudinally directedangularly spaced agitator or riser bars 252 each extending the fulldistance between weirs and each of height approximately half that of theweir. As the kiln rotates, the agitator bars 252 stir the bed materialand expose fresh bead material to the furnace atmosphere. In addition,some of the beads in each zone are carried by the agitator bars to anupper region of the kiln and as the kiln continues to rotate allowed tofall as a cascade back to the bottom of the kiln. This cascade of beads,which is not a feature of current commercially used carbonizing oractivating kilns, promotes contact between the material being carbonisedor activated and the furnace atmosphere and hence speeds theseoperations. The counter-current flow 239 of steam or other activatinggas through the kiln is, as previously stated, at relatively low linearvelocity and is insufficient to interfere with the cascading beadssubstantially returning to the treatment zone in which they haveoriginated. Activation in the present kiln can be achieved within a fewhours, whereas in a conventional commercial kiln, about 5 days areneeded to complete this operation.

In operation, there are three principal regions of the kiln. At theupstream end, there is a region where residual ethylene glycol and othersolvent is removed endothermically. This may approximately be equatedwith region 241 a, which should operate at no more than about 300° C. inthe case of mesoporous resin beads, preferably about 200-250°, becausemesoporosity is progressively lost as temperatures in the feed zone 241a rise above 300° C. Rapid temperature increase follows up to atemperature of about 850° C. as the beads progress to carbonization zonewhich may be roughly equated with region 241 b. The resin of the beadsis exothermically converted to char, with evolution ofhydrogen-containing gaseous products including monomeric species andoligomeric species of molecular weight e.g. up to about 500. The streamof steam and carbonization gas products carries the evolved gaseousproducts towards line 224, and optical inspection of the beads at thisposition in the kiln indicates that they appear white hot. Thedownstream end of the kiln, roughly defined by zones 241 c-241 dcorresponds roughly to an endothermic activation region where thesurface area within the now carbonised beads is increased by removal ofcarbon in the micropores by the reactions:

C+H₂O→CO+H₂ or

CO₂+C→2CO.

The material at this end of the furnace no longer glows white hot, butmaintenance of temperatures in the range 800-850° C. is desirable toenable activation to proceed e.g. about 800°. As the activated carbonleaves the portion of the furnace body 202 within the housing 204, itbecomes cooled rapidly to about 150° C. by the incoming steam. It canthen be collected as indicated.

The product is an activated carbon in bead form with low fines contentboth a mesoporous/microporous structure and a high active surface area.

Various modifications and variations of the described aspects of theinvention will be apparent to those skilled in the art without departingfrom the scope and spirit of the invention. Although the invention hasbeen described in connection with specific preferred embodiments, itshould be understood that the invention as claimed should not be undulylimited to such specific embodiments. Indeed, various modifications ofthe described modes of carrying out the invention which are obvious tothose skilled in the relevant fields are intended to be within the scopeof the following claims.

1. A process for producing discrete solid beads of polymeric material,said process comprising: forming a combined stream from a stream of apolymerizable liquid precursor and a stream of a liquid dispersionmedium with which the liquid precursor is substantially or completelyimmiscible; treating the combined stream so as to disperse thepolymerizable liquid precursor as droplets in the dispersion medium;allowing the droplets to polymerise in a laminar flow of the dispersionmedium so as to form discrete solid beads that cannot agglomerate; andrecovering the beads from the dispersion medium, the dispersivetreatment time being short compared to the laminar flow polymerizationtime so that agglomeration of the liquid precursor during dispersivetreatment is substantially avoided.
 2. The process of claim 1, whereinthe stream of polymerizable liquid precursor comprises polymerizablecomponents in solution in a first polar organic liquid, and the liquiddispersion medium comprises a second non-polar organic liquid, the firstand second organic liquids being substantially immiscible.
 3. Theprocess of claim 2, wherein the first organic liquid is ethylene glycolor diethylene glycol and the second organic liquid is mineral oil ortransformer oil. 4-7. (canceled)
 8. The process of claim 1, furthercomprising: forming the polymerizable liquid precursor by combining andmixing first and second component streams thereof in an in line mixer.9. The process of claim 8, wherein the first component stream comprisesa phenolic nucleophilic component dissolved in a pore former and thesecond component stream comprises a cross-linking agent dissolved in thepore former, wherein the pore former is ethylene glycol, the phenolicnucleophilic component is a novolac with a molecular weight of less than1500, and the cross-linking agent comprises hexamethylenetetramine,melamine or hydroxymethylated melamine. 10-14. (canceled)
 15. Theprocess of claim 8, which comprises supplying the first and secondstreams from respective first and second vessels by pressurising saidvessels.
 16. The process of claim 8, which comprises supplying the firstand second streams from respective first and second vessels usingnon-pulsating pumps, wherein the non-pulsating pumps are gear or rotaryvane pumps. 17-18. (canceled)
 19. The process of claim 8 wherein mixingthe combined first and second component streams in the in-line mixer isat a temperature greater than or equal to 20° C. below the laminar flowpolymerization temperature where polymerization to give a solid particleis complete in less than 2-4 minutes, wherein the temperature of thestream of liquid dispersion medium is less than or equal to 10° C. belowthe laminar flow polymerization temperature prior to combination withthe stream of polymerizable liquid precursor. 20-27. (canceled)
 28. Theprocess of claim 1 wherein the dispersion treatment is carried out in anin-line mixer.
 29. The process of claim 28, wherein the dispersiontreatment is carried out under turbulent conditions or transitionturbulent conditions, wherein the volume flow rate of the stream ofliquid dispersion medium is 3-10 times that of the polymerizable liquidprecursor, wherein the combined stream treatment is completed so as todisperse the polymerizable liquid precursor as droplets in thesuspension medium within 0.2-5 secs, wherein the combined stream istreated to form droplets which give rise to polymer beads of volumeaverage size in the range 100-1000 μm, wherein the combined stream istreated to form droplets that give rise to polymerized beads having aD90/D10 particle size distribution less than or equal to
 10. 30.(canceled)
 31. The process of claim 1, further comprising: supplying thestream of liquid dispersion medium having the polymerizable liquidprecursor dispersed as droplets to a vertical polymerization columnhaving a descending flow of liquid suspension medium, the density of thedroplets being greater than the density of the liquid suspension medium.32. The process of claim 31, wherein the dispersion medium descends thecolumn in 0.5-1.5 hours and dispersed droplets of mean size ˜400 μmdescend the column in an average time of about 1-5 minutes. 33-34.(canceled)
 35. The process of claim 1, further comprising: collectingpolymerized beads from the polymerization column in a collection vesselby sedimentation or by centrifugation; recycling dispersion medium fromwhich polymerized beads have been recovered; washing the centrifugedbeads with water to remove pore-former; and vacuum drying the beads torecover pore-forming solvent and recycling the recovered pore-formingsolvent for production of hexamine/solvent solution and/or resin/solventsolution. 36-39. (canceled)
 40. Apparatus for forming discrete solidbeads of polymeric material, said apparatus comprising: a first line forconveying a stream of a polymerizable liquid precursor; a second linefor conveying a stream of a dispersion medium with which thepolymerizable liquid precursor is substantially or completelyimmiscible; an in-line mixer configured to receive a combined flow fromthe first and second lines and to disperse the polymerizable liquidprecursor as droplets in the dispersion medium; a verticalpolymerization column configured to receive the dispersion medium withthe droplets dispersed therein and to permit the polymerizable liquidprecursor polymerize while descending the column in a descending flow ofpolymerization medium; and a vessel at the base of the column forreceiving the descending flow of dispersion medium and collectingpolymerized solid beads.
 41. The apparatus of claim 40, furthercomprising: first and second vessels for storage of first and secondliquid components of the polymerizable liquid precursor; first andsecond component lines for conveying the liquid components; first andsecond non-pulsating pumps in said lines for conveying component streamsthrough the lines; and a second in-line mixer configured to receive andmix the streams of the first and second components and to form apolymerizable liquid precursor stream.
 42. (canceled)
 43. The apparatusof claim 41, further comprising a heater in at least one of the firstand second component lines for heating the stream flowing to the secondin-line mixer; a storage vessel for dispersion medium, a line leadingfrom the storage vessel to the in-line mixer, and a third non-pulsatingpump in said line for conveying a stream of dispersion medium; a thirdin-line mixer configured to receive heated dispersion medium from theheat exchanger and to supply dispersion medium that has passed throughit to the first in-line mixer, wherein the dispersion medium linecomprises a heat exchanger for heating the stream of dispersion mediumfrom the storage vessel, wherein the vessel at the base of the column isa settling tank having an outlet for beads forming a sediment in saidtank and at least one of the non-pulsating pumps is a gear or rotatingvane pump. 44-48. (canceled)
 49. The process of claim 1, furthercomprising carbonizing and activating the beads by supplying the beadsto an externally fired rotary kiln maintained at carbonizing andactivating temperatures, the kiln having a downward slope to progressthe material as it rotates, the kiln having an atmosphere substantiallyfree of oxygen provided by a counter-current of steam or carbon dioxide,and annular weirs being provided at intervals along the kiln to controlprogress of the beads. 50-54. (canceled)
 55. The process of claim 49wherein the kiln is provided with 5-10 weirs along its length, whereinthe beads form a bed, portions of which are lifted and cascaded throughthe kiln atmosphere by longitudinally directed angularly spaced liftbars extending between weirs, wherein the lift bars have a height abovean internal cylindrical surface of the kiln which is approximately 50%of the height of the weirs, wherein the kiln has an entry regionconfigured to dry or remove solvent from the beads and maintained at atemperature not more than 300° C., wherein superheated steam at about150° C. is introduced at the discharge end of the kiln and flowscounter-current to the beads to provide the kiln atmosphere and the isconfigured to provide a residence time for the beads of 2-5 hours.56-76. (canceled)
 77. A method for carbonizing and activatingcarbonaceous material, comprising: supplying carbonaceous material to anexternally fired rotary kiln maintained at carbonizing and activatingtemperatures, the carbonaceous material comprising material of vegetableorigin or mesoporous phenolic resin beads and the kiln having a downwardslope to progress the carbonaceous material as it rotates, the kilnhaving an atmosphere substantially free of oxygen provided by acounter-current of steam or carbon dioxide, and annular weirs beingprovided at intervals along the kiln to control progress of thematerial, wherein the activated carbon product has macropores, mesoporesand micropores.